A single-field index indexes one field. It is useful when queries frequently filter or sort by that field.

Create an ascending index with db.collection.createIndex({ field: 1 }) and a descending index with { field: -1 }. For a single-field index, MongoDB can often traverse the index in either direction for simple ascending or descending sorts. The direction becomes more important in compound indexes.

A single-field index on status can support eligible filters on status. An index on createdAt can support eligible date-range filters and sorts. Whether an index is beneficial depends on selectivity, query shape, and the amount of data returned.

Before adding an index, examine the application's real filters, sort fields, projection, frequency, and latency requirements.

db.orders.createIndex({ status: 1 });
db.orders.createIndex({ createdAt: -1 });

// Check indexes on the collection.
db.orders.getIndexes();